NOTES
AND
COMMENT
CONCENTRATIONOF PARTICULATE CARBOHYDRATEATTHE HALOCLINE
IN CHESAPEAKE
BAYS
Organic matter in water occurs in true
solution, colloidal solution, and suspension.
Suspended carbohydrate in the water column is divided into living matter and
detritus. Of the detritus, some is produced
in the area and some comes in from other
carbohydrate,
in
areas. The particulate
either form, may 1) serve as food for larger
organisms, 2) settle out of the water, 3) be
converted to dissolved carbohydrate,
or
4) be carried away from the area by water
As an example of the first
movement.
situation, oysters and other animals can
use small carbohydrate particles for food
( Haven 1965). Some is converted to
dissolved carbohydrate by bacterial action
(Duursma 1960) or at the death of phytoplankton
(Collier
1958; Guillard
and
Wangersky 1958 ) , and particulate carbohydrate is known to be present in sediments ( Bordovskiy 1965a, b, c ) .
In the Chesapeake, the upper layer of
the water column contains more oxygen,
is less saline, and, during summer, is
warmer than the deep water. There is a
net nontidal flow of the deeper water
toward the head of the bay and of the
surface water toward the ocean, providing
a zone of no net flow at the boundary
between these layers. A thermocline and
halocline are strongly developed during
summer and vary in definition and position
with weather conditions ( Prichard 1953).
Our primary interest was centered on the
effectiveness of the halocline as a barrier
to sinking of organic aggregates from the
overlying water. If the density differential
above and below the halocline is sufficient
to slow down the sinking rate of seston
1 Contribution
No, 347, Chesapeake Biological
Laboratory,
Solomons, Maryland.
Research partially supported by the University
of Maryland and
by the National Science Foundation
Undergraduate Research Participation
Program under Grant
No. GY-843.
significantly,
then one would expect a
higher concentration of organic material at
the halocline.
MATEXUALS AND METHODS
Water samples were collected from a
column approximately
31 m deep in the
channel near Hooper’s Island Light ( 38”
15’ 30” N lat, 76” 16’ 00” W long), midway
in the Chesapeake Bay. The level of the
halocline was defined, and sampling was
intensified in that region. Samples were
taken with a e-liter Kemmerer bottle or a
submersible pump and stored in 500-ml
polyethylene
bottles under refrigeration
until
filtration.
Samples were swirled
before filtration
to resuspend particulate
material, and a lOO-ml sample was filtered
at 20-cm vacuum through a glass-fiber filter
of 0.2-p effective pore size. After filtration,
the pads were frozen until carbohydrate
analyses were performed.
Analysis for carbohydrate was modified
from the technique
of Strickland
and
Parsons ( 1965). Th e method used depends
on a quantitive reaction of carbohydrate
with anthrone in sulfuric acid. The reagent
was kept in a dark glass bottle and refrigerated when not in use. Ten ml of anthrone
reagent were added by pipette to a centrifuge tube containing the sample on a filter
pad; the sample was then heated in a
constant temperature bath at 94C for 7
min and cooled to 5C. The extinction of
the resulting colored solution of furfuran
and its homologues (Dische 1962) was
measured at 6,200 A in a spectrophotometer
(Hitachi
Perkin-Elmer
139 UV-VIS).
A
sucrose solution of 0.01 gm/ml was used
as a standard. Replicate analyses of the
sucrose standard indicated an accuracy of
*50 mg/m3 at an initial concentration of
500 mg/m3.
Chlorophyll-carotenoid
determinations,
also using Strickland and Parsons method
( 1965) were performed on l-liter samples
169
NOTES AND COMMENT
OF
::
SALINITY
IS
‘?
SALINITY
%.
9,
z#$
20
I
5-
1 Aug
30
21 July
I
350
CARBOHYDRATE
MGM
::
1;
t
1
J
IMO
600
CARBOHYDkE
SALINITY
o-
1
,I
”
’
1966
1966
M:?i
’
%
20
25
70
5-
IO-
25-
30-
8
35
Aug
:,
1966
’
I
600
I
800
C~ARBOHYDRATE
FIG. 1. Vertical
mer 1966.
distribution
MG
J
loo0
h4 f
of particulate
carbohydrate
from the water column. The samples were
filtered on glass-fiber filters and extracted
with 6 ml of 90% acetone.
Salinity was determined using a hydrometer or electrodeless induction salinometer.
RESULTS
High concentrations of suspended carbohydrate occurred at the surface and at or
near the halocline ( Fig. 1).
(-)
and salinity
(------)
during
sum-
On 15 July 1966, the carbohydrate concentration at the surface was 69’7 mg/m3,
the concentration at the halocline (5-8 m)
was 529 mg/m3, and a typical value was
330 mg/m3. On 21 July 1966, the halocline
was located at 14 m, and carbohydrate at
that depth was 910 mg/m3 while at 13 and
15 m it was considerably lower (659 and
695 mg/m3). The halocline was located at
approximately 10 m on 1, 8, and 15 August,
171
NOTES AND COMMENT
and correspondingly
high carbohydrate
concentrations were again associated with
it. In addition to the concentration
of
particulate carbohydrate in the vicinity of
the halocline, there also appeared to be a
similar concentration at about 6 m. There
was no significant
correlation
between
chlorophyll and particulate carbohydrate in
any samples examined.
DISCUSSION
Phytoplankton in the water column are
suspended at depths at which their density
approximates that of the suspending medium. At death, their density is changed
by the breakdown of their cell walls and
they sink until they reach a level of neutral
buoyancy or the bottom, assuming that
they are not removed from the system. At
the halocline, this detritus accumulates
until its density equilibrates with that of
the underlying water. Since the detritus is
not all of the same density, it settles to
and from this region at varying rates. The
assumption that the matter is of differing
densities is supported by the fact that
there are different densities at the halocline
on different days, but a concentration of
particulate
carbohydrate
is still present.
Microscopic examination of the particulate
matter collected on the filters indicated
that the material was composed of light
brown aggregates approximately l-2 p in
planar dimensions, similar to those described by Riley ( 1963). Living zooplankton do not seem to contribute
to the
particulate
carbohydrate
since no zooplankton were observed on the filters
during microscopic examinations, although
they were observed in surface samples.
The persistence of the high particulate
carbohydrate concentration at or near the
halocline indicates that the halocline acts
as a temporary barrier to the sinking of
organic aggregates. The values obtained
below the halocline indicate that the carbohydrate is not entirely used as food by
organisms in the water column.
High concentrations of particulate carbohydrate occur regularly at the surface of
the water and in the zone of the halocline.
CONCLUSION
The region of the halocline provides a
zone of no net flow and a density change
that traps particulate organic matter as it
sinks through the water column. This matter is predominately
detritus.
Physical
solution and use by organisms do not
completely reduce the particulate
carbohydrate fraction while the matter is still
in the water column.
ROBERT B. BIGGS
CAROLYN D. WETZEL
Chesapeake Biological Laboratory,
University of Ma yland,
Box 38,
Solomons, Maryland
20688.
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Sources of organic
BORDOVSKIY, 0. K. 196%.
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Marine Geol., 3:
5-31.
1965b.
Accumulation
of organic mat-.
ter in bottom sediments.
Marine Geol., 3:
-.
33-82.
196%.
Transformation
of organic matter in bottom sediments and its early diagenesis. Marine Geol., 3: 83-114.
aspects of
COLLIER, A. 1958. Some biochemical
red tides and related oceanographic
problems. Limnol. Oceanog., 3: 33-39.
DISCHE, Z. 1962. Color reactions of carbohyIn R. L. Whistler [ed.],
drates, p. 477-512.
AcaMethods
in carbohydrate
chemistry.
demic, N.Y.
DUURSMA, E. K. 1960. Dissolved
organic carand phosphorus
in the sea.
bon, nitrogen
Neth. J. Marine Res., 1: 1-148.
GUILLARD, R. L., AND P. J. WANGERSKY. 1958.
of extracellular
carbohyThe production
drates by some marine flagellates.
Limnol.
Oceanog., 3 : 449454.
feeding of
HAVEN, D. S. 1965. Supplemental
oysters with
starch.
Chesapeake
Sci., 6:
43-51.
1953.
Salinity
distribution
PRICHARD, D. W.
and circulation
in the Chesapeake Bay estuarine system.
J. M arine Res., 11: 106-123.
RILEY, G. A. 1963. Organic aggregates in seawater and the dynamics of their formation
and utilization.
Limnol. Oceanog., 8: 372381.
STRICKLAND, J. D. H., AND T. R. PARSONS. 1965.
A manual of sea water analysis.
Bull. Fisheries Res. Board Can. 125, 2nd Ed. 203 p.